In the manufacture and repair of the typical bearing assemblies for a shaft and housing through which high axial loads are imposed and radial forces are encountered, the cumulative tolerances attributable to manufacture of the various components has posed problems.
Particularly under circumstances when the bearing assembly operates in a hostile environment, such as the environment encountered when drilling bore holes in the earth, such as in well drilling, mining, pipeline installation, or the like, the cumulative manufacturing tolerance, as well as unequal wear of the parts has been a problem.
For example, in the drilling of bore holes in the earth using an in-hole fluid motor to drive a drill bit, the drill bit is attached to the shaft which is driven by the fluid motor. The shaft is hollow to allow the circulation of the drilling fluid through the motor to drive the shaft and through the shaft to the bit to flush cuttings from the bore holes and cool the bit. Whether the drilling fluid is gas, air, or liquid, the fluid can contain very erosive particles which can cause bearing wear when the fluid flows through the bearings to also cool the bearings. In any event, the effective penetration of the drill bit through the earth formation is dependent upon the application of axial loading or weight on the bit cutters, the load or weight being transmitted to the drive shaft through the bearings from the housing. In such bearing assemblies, it is customary to employ spring elements to provide a spring cushion and absorb shock during operation of the drill.
When the bearings do not or cannot collectively transmit the load, and only certain bearings transmit all of the load excessive wear and ultimate destruction of the overloaded bearing may result. Such an event can cause cessation of the drilling operation and retrieval of the drilling apparatus for bearing repair, long before the drill bit may require change, and the drilling operation is thus terminated in an uneconomic period of time in the hole. On the other hand, when, during such a drilling operation, the bit is off bottom, while drilling fluid is being circulated, the drive shaft is supported by bearings in the housing which may also wear excessively if the bearings are overloaded by the piston effect of fluid acting to force the drive shaft from the housing. An example of the prior art is seen in U.S. Pat. No. 3,936,247, granted Feb. 3, 1976.
In pending U.S. patent application, Ser. No. 914,271; filed June 9, 1978; adjustably positioned bearing sub-assemblies, in a stacked bearing assembly, are disclosed to substantially eliminate tolerance in the bearing sub-assembies, so that each of them will transmit its share of the load between a relatively rotatable shaft and housing. Not only is that invention useful in eliminating cumulative manufacturing tolerances in the stacked bearing assembly, but also the invention enables the bearing assembly to be maintained by taking up tolerance which occurs due to wear during use. Taking up the tolerance in the bearing sub- assemblies also assures that the springs are all active, during use, to cushion the shock and cyclic loading caused during a drilling operation.
As disclosed in the above-identified application, a stacked bearing assembly is provided wherein a plurality of bearing sub- assemblies are disposed between the housing and the shaft, and, the sub-assemblies each include an adjustable stop or shoulder on the shaft movable towards and away from a shoulder in the housing, whereby the several bearing components can be moved into engagement with one another regardless of the tolerance between the parts, whether new or used. The bearing sub-assemblies include thrust and radial bearings and springs between the shaft and the housing of the assembly, shock and vibration are dampened, and the shaft is centralized in the housing.
As is known, means are incorporated in such assemblies to allow the flow of a minor portion of the erosive fluid through the assembly or the assembly may be sealed.